Most places will charge your stay according to the length, so, why not make that TOTAL living space instead of paying for the empty space of your tongue?
I have never been to any campground, either private or public, that charges by the length. That practice seems to be common to boat marinas but not campgrounds. The campground owners will often ask how long your rig is but it is not for the purpose of charging. It is for trying to fit your rig into a large enough site.
In addition, many campgrounds have various prices on their sites but it is not necessarily based on length. Some may be waterfront, some have more anemities, some closer to the pool, some 50amp, etc. etc. etc.
Barney
In 30 yrs. of Rving, I have never been charged by the length of my rv. Yes they will ask you what your length is but only so they find you a site that will accomadate your length. Not all rv sites in every rv park are 50' in length, there is a variety of lengths in every rv park:)
x2. In over 45 years of camping I have never been charged for length. Laundry, yep, showers, yep, sewer, yep, more people than 2, yep; but never length.